The use of sutures and meshes made from absorbable polymers has been disclosed in numerous patents for the past four decades. However, over the past three decades, the use of absorbable fibers in fibrous composites has been limited for the most part to bicomponent composites for use in (1) solid fiber-reinforced orthopedic devices, and to a lesser extent, (2) synthetic absorbable vascular grafts. Availability of new types of fiber-forming and microfiber-forming absorbable polymers led to the development, in this laboratory, of a number of fibrous and microfibrous medical constructs having a broad range of properties. These include (1) fully or partially absorbable composites for urological and vascular applications [U.S. Pat. No. 7,371,256 (2002); U.S. patent application Ser. No. 10/860,677 (2003); U.S. patent application Ser. No. 11/175,635 (2005); U.S. patent application Ser. No. 11/204,822 (2005); and U.S. patent application Ser. No. 11/346,117 (2006)], and fully or selectively absorbable knitted meshes [U.S. patent application Ser. No. 11/886,370 (2007); U.S. patent application Ser. No. 11/978,795 (2007); U.S. patent application Ser. No. 11/983,321 (2007)]. However, none of these composites was claimed as having permeability-modulated barrier properties to allow their application as medical devices or components thereof for use in conjunction with the surgical procedures noted in the present invention. Most important among such procedures are those dealing with prosthetic dura mater and patches for repairing the urinary bladder and vascular tissue and/or their tissue engineering. Accounts of the prior art related to the area are described below.
In a disclosure on bladder reconstruction that is pertinent to the instant invention (U.S. Pat. No. 6,576,019) the inventor provided a useful background to his invention, excerpts of which are summarized below:
The human urinary bladder is a musculomembranous sac situated in the anterior part of the pelvic cavity and serves as a reservoir for urine, which it receives through the ureters and discharges through the urethra. The bladder ureters and urethra are all similarly structured in that they comprise muscular structures lined with a membrane comprising urothelial cells coated with mucus that is impermeable to the normal soluble substances of the urine. The bladder tissue is elastic and compliant. That is, the bladder changes shape and size according to the amount of urine it contains. A bladder resembles a deflated balloon when empty but becomes somewhat pear-shaped and rises in the abdominal cavity when the amount of urine increases.
The bladder wall has three main layers of tissues: the mucosa, submucosa, and detrusor. The mucosa, comprising urothelial cells, is the innermost layer. The submucosa lies immediately beneath the mucosa and its basement membrane. It is composed of blood vessels which supply the mucosa with nutrients and the lymph nodes which aid in the removal of waste products. The detrusor is a layer of smooth muscle cells which expands to store urine and contracts to expel urine. The bladder is subjected to numerous maladies and injuries which cause deterioration which may result from infectious diseases, neoplasms and developmental abnormalities. Further, bladder deterioration may also occur as a result of trauma such as, for example, car accidents and sports injury.
Although a large number of biomaterials, including synthetic and naturally derived polymers, have been employed for tissue reconstruction or augmentation, no material has proven satisfactory for use in bladder reconstruction. For example, synthetic biomaterials such as polyvinyl and gelatin sponges, polytetrafluoroethylene, and silastic patches have been relatively unsuccessful, generally due to foreign body reactions. Other attempts have usually failed due to mechanical, structural, functional, or biocompatibility problems. Permanent synthetic materials have been associated with mechanical failure and calculus formation. Naturally derived materials such as lyophilized dura, deepithelialized bowel segments, and small intestinal submucosa have also been proposed for bladder replacement. However, it has been reported that bladders augmented with dura, peritoneum placenta, and fascia contract over time.
In an effort to circumvent the drawbacks of the prior art disclosed in, Atala, U.S. Pat. No. 6,576,019 (2003) a device comprising a biocompatible synthetic or natural polymeric matrix shaped to conform to at least a part of the luminal organ or tissue structure with a first cell population on or in a first area and a second cell population such as a smooth muscle cell population in a second area of the polymeric matrix. The method involves grafting the device to an area in a patient in need of treatment. The polymeric matrix comprises a biocompatible and biodegradable material.
In a second disclosure pertinent to the instant invention on artificial dura mater, Yamauchi et al. [U.S. Pat. No. 7,041,713 (2006)] provided a useful background to the subject of this invention, excerpts of which are summarized below with necessary editing to facilitate readability.
The dura mater is located between the cranium and the brain and around the spinal cord. It principally protects the brain and spinal cord and prevents cerebrospinal fluid leakage. Defects or contractures of the dura mater need to be compensated for and lyophilized human dura mater has been used for that purpose. However, human dura mater has drawbacks such as low homogeneity and limited supply. Further, possible transmission of Creutzfeldt-Jakob disease through the use of human dura mater has been reported. To solve the above noted problems, an artificial dura mater made of silicone was developed. However, silicone dura mater has fallen into disuse as it was reported that silicone dura mater creates a predisposition to meningorrhagia by remaining permanently in vivo because it is non-biodegradable, chronically stimulating the surrounding tissue and causing hypertrophy of the granulation tissue. In contrast, artificial dura maters made of biodegradable and bioabsorbable materials such as collagen were produced but they are not in practical use because of strength-related problems, i.e., because their suture strength is insufficient to allow them to be sutured integrally with the dura mater.
This led Yamauchi et al [U.S. Pat. No. 7,041,713 (2006)] to conceive an artificial dura mater, which comprises an amorphous or low crystallinity polymer as a constituent component and which prevents the cerebrospinal fluid leakage. More specifically, these inventors described a method for preparing an artificial dura mater which is formed as an integral molding of an amorphous or low crystallinity polymer and a structural reinforcement wherein the amorphous or low crystallinity polymer and the structural reinforcement are integrated by bonding, fusion or impregnation, the amorphous or low crystallinity polymer having (1) a degree of crystallinity of 20 percent or lower; (2) an elastic modulus at 4 percent extension of 10 MPa or lower; (3) a Tg of 15° C. or lower; (4) a tensile elongation at break of 200 percent or greater; (5) an elastic modulus at 37° C. of 1×108 Pa or less; and (6) a ratio of relaxation elastic modulus at 23° C./elastic modulus at 37° C. of 0.3 or greater. Meanwhile, the structural reinforcement was described as having (1) an elastic modulus at 5 percent extension of greater than 10 MPa; (2) a Tg of higher than 15° C.; and (3) a tensile elongation at break of less than 200 percent. Furthermore, the amorphous or low crystallinity polymer was noted as having a weight of 10 to 98 percent of the total weight of the integral molding, and the structural reinforcement having a weight of 2 percent or more of the total weight of the integral molding. The method of preparing said artificial dura comprises the step of integrating the amorphous or low crystallinity polymer and the structural reinforcement by bonding, fusing or impregnating to give an integrally molded artificial dura mater.
In a disclosure of general pertinence to the present invention on pelvic floor construction, Tripp et al. [U.S. Pat. No. 6,197,036 (2001)], provided a background to their invention, excerpts of which appear below.
Damage to the pelvic floor is a serious medical condition which may occur during delivery or due to injury to the vesicovaginal fascia. Such an injury can result in a herniation of the bladder called a cystocele. Other similar conditions are known as rectoceles, enteroceles, and enterocystoceles. A rectocele is a herniation of the rectum. An enterocele is formed when the intestine protrudes through a defect in the rectovaginal or vesicovaginal pouch and an enterocystocele is a double hernia in which both the bladder and the intestine protrude. These herniations are serious medical problems that can severely and negatively impact a patient both physiologically and psychologically. Treatment of these conditions requires repositioning of the protruding organs or portions thereof. Existing tissue is often compromised facilitating the need to use a synthetic patch. Current medical procedures for repositioning the protruding organs or portions thereof may be time consuming or invasive. Hence, there is a need for reducing the amount of time which these procedures require and the invasiveness of the procedures. Accordingly, Tripp et al (U.S. Pat. No. 6,197,036 (2001)) disclosed that herniation, including cystocele, rectocele, and enterocystocele may be treated with prefabricated repair patches. The repair patches include a natural or synthetic biocompatible material having a shape adapted to support herniated tissue. The patch also contains a plurality of apertures positioned in the central plane of the patch which may permit ingrowth and may also be an attachment site for fixing sutures. The patch may be covered with coating to decrease the possibility of infection, and/or increase biocompatibility. The coating may also include one or more drugs, for example, an antibiotic, an immunosuppressant, and/or an anticoagulant.
In a second disclosure of general pertinence to the present invention on the use of reinforced foam implants with enhanced integrity for soft tissue repair and regeneration, Binette et al. [U.S. Pat. No. 6,884,428 (2005)] described a biocompatible tissue repair stimulating implant or “scaffold” device that is used to repair tissue injuries, particularly injuries to ligaments, tendons, and nerves. Such implants are especially useful in methods that involve surgical procedures to repair injuries to ligament, tendon, and nerve tissue in the hand and foot. The repair procedures may be conducted with implants that contain a biological component that assists in healing or tissue repair.
Reviewing the above noted disclosures of the prior art show clearly the absence of any absorbable permeability-modulated barrier composites and their use as novel prosthetic devices or for the prevention of adhesion formation. This provided an incentive to explore the new features associated with the instant invention.